1. Field of the Invention
The present invention relates to a method and a machine for grinding a cylindrical surface of a workpiece with a grinding wheel.
2. Discussion of the Prior Art
In a conventional grinding machine for traverse feed grinding, a grinding wheel has a straight grinding surface and a tapered grinding surface successive thereto. The straight grinding surface is parallel to the rotational axis of a workpiece to be ground, while the tapered grinding surface forms a predetermined angle with the rotational axis of the workpiece. When a cylindrical surface of the workpiece is ground with this grinding wheel, the grinding wheel is advanced at the position corresponding to one end of the workpiece so as to be fed into the workpiece. Then, the workpiece is traversed in a direction of its rotational axis. During this operation, the tapered grinding surface carries out rough grinding and subsequently, the straight grinding surface carries out fine grinding.
Since the grinding machine having such a grinding wheel can complete the grinding operation for the cylindrical surface of the workpiece through only one traverse feed, the time required for the grinding operation can be shortened. However, there are involved some problems regarding the above-mentioned grinding wheel.
In the case where the angle which the tapered grinding surface and the rotational axis of the workpiece W make is too large, the width A of the tapered grinding surface which acts on the workpiece W is narrow, as shown in FIG. 1(a). Under this condition, excessive loading acts on each grain of the tapered grinding surface, whereby abrasion of the grinding wheel G and grinding resistance become large. Conversely, in the case where the angle is too small, the width A is wide, as illustrated in FIG. 1(b). Each grain on the tapered grinding surface is subjected to a slight load which causes the grinding wheel G to slide or slip on the cylindrical surface of the workpiece W. Since these phenomena influence roundness and straightness of the ground workpiece W, it is difficult to attain desired roundness and straightness.
Further, the straight grinding surface of the grinding wheel G works to smooth the cylindrical surface of the workpiece W. If the length of the straight grinding surface is too short, it is difficult to attain a desired surface roughness.